The present invention relates to a power supply system including a plurality of power units connected to the common bus for supplying power to a plurality of electronic apparatus.
In FIG. 1, showing the conventional power system of this type, reference number 1 denotes a power unit providing a specified voltage, e.g., 5 volts, with its 5-volt output (5P) and 0-volt output (GND) connected to a 5-volt bus 6 and GND bus 8, respectively, and 2 denotes another power unit providing a specified voltage other than that of the power unit 1, e.g., 24 volts, with its 24-volt output (24P) and 0-volt output (GND) connected to a 24-volt bus 7 and GND bus 8, respectively. On the buses 6, 7 and 8, there are connected a plurality of electronic apparatus, e.g., control units 3, 4 and 5 of control system, and power is supplied to these units through the 5-volt input (5P), 24-volt input (24P) and 0-volt input (GND).
The power units 1 and 2 have contacts 1X and 2X, respectively, each of which becomes conductive when the unit operates normally. The contacts 1X and 2X are connected in series so that the output is provided at 9X when both contacts are conductive, i.e., when both power units 1 and 2 operate normally. If one of the power units fails, the output 9X goes off, and thus the operation of the power units can be verified by monitoring the output 9X.
In such conventional power system, however, if the power consumption of control units increases or the number of control units is increased, the capacity of the power units must be increased, and therefore, the power system needs to be designed for each arrangement of control units, resulting in a poor productive efficiency of the power system. In addition the conventional power system has a drawback that a failure of a power source unit can cause directly the failure of the control system.